Working pressure in the water supply system: what should it be and how to increase it

Instrumentation at the water supply input to the house

Normal pressure in heating systems, cold and hot water supply, allows them to work with maximum efficiency. That is why when designing these networks it is very important to focus on water supply pressure standards.

If the pressure is below optimal, using the water supply will become inconvenient or even impossible. And if it is higher, there is a risk of failure of working units and water dispensing devices.

You will learn from this article what you need to know and do to optimize the operation of such systems.

What it is?

In order for the water supply system to function properly, water supply services constantly maintain a certain pressure in it.
Pressure is measured by a physical quantity equal to the force of water acting on the walls of the pipeline.

With its help, the water supply is achieved in such a state in which it will fully function without the risk of emergency situations:

1. burst pipes,
2. shut-off valves
3. various plumbing equipment.

Reference! People call pressure pressure. And although these concepts are not identical, their essence is the same. Pressure is one of its many designations.

Causes of weak and excessive pressure

Most often, a decrease in water pressure occurs due to natural wear and tear of the pipeline. In addition, if metal pipes were used to lay it, then over time the pressure will decrease due to corrosion.

The problem may also be the presence of limescale on the walls of the pipes. It appears due to too hard water.

Reasons for low pressure are also:

1. 
   Pressure installation that does not comply with system parameters.
   Very often, in autonomous water supply systems, water has to be lifted from fairly deep aquifers. Then bring it to consumers located at a great distance from the station, and even at different heights. If the power of the pumps does not correspond to this situation, the pressure will be weak.

2. Low resource of the well itself from which water is taken. Even if initially everything was normal, the source gradually becomes empty and the pressure decreases.
3. The emergence of new water intake points that can work simultaneously - for example, they also purchase a dishwasher or a whirlpool bath. If their appearance was not taken into account in the project, then now you will have to redo it, perhaps buy additional equipment.

In case of excessive water pressure, two options are possible - either the equipment was selected with too much power reserve, or there is an air lock inside the system.

Designation of pressure in the pipeline

Traditionally, pressure is measured in Pascals (Pa), but in the water supply industry other conventions are also accepted, and they differ in different countries:

• In Russia, pressure is usually measured in kgf/cm². 100 kgf/cm² is identical to 980.67 Pa.
• In European countries, another conventional unit is used - bar, which is equal to 10⁵ Pa.
• In England and the USA, the designation psi is used, which corresponds to 6.87 kPa.

Pressure is also measured in technical atmospheres and millimeters of mercury.

For your information. A water pressure of 1 bar corresponds to 1.02 atmospheres and is equivalent to 10 meters of water column.

The relationship between the values ​​of different designations is given in the following table:

Methods for increasing pressure

There are several methods for increasing the water pressure in a water supply system. Let's look at the most effective ones:

1. Installation of an intermediate pump. If the system is quite long, the pump, which is installed in the well itself, cannot cope with the load. As a result, in remote areas the flow rate can drop significantly. To solve this problem, an intermediate pump is installed, for example, near the connection between the external and internal systems.
2. If a modern boiler is installed in the house, then an additional pump is installed only on the cold circuit. This recommendation is due to the fact that the boiler itself may have an element that circulates hot liquid.
3. The installed pumps can operate in both manual and automatic modes. The most popular models are those that can operate autonomously from installed pressure sensors. Automation can not only control the operation of devices, but also protect them from high loads.
4. If the water level in the well can drop significantly, a pumping station is installed. It differs from a conventional pump in that it has a storage tank. Several tens or hundreds of liters of water can accumulate in the tank, which is supplied to the pipeline when the pressure drops. At the moment when water consumers are not open, it is raised and the tanks are filled.

Of course, if the well depth is small, as is the productivity indicator, then no devices will solve the problem. Therefore, when designing a water supply system in a suburban area, much attention is paid to the occurrence of groundwater levels or underground sources.

Dependence of speed on pressure

In water supply, there is one very important relationship - the dependence of pressure on the speed of water in the pipeline. This property is described in detail in Bernoulli's physical law. We will not consider it in detail, but we will only point out its essence - as the speed of water flow increases, its pressure in the pipe decreases.

It so happens that not all plumbing fixtures are designed for operation at high pressure ; in most cases they are limited to 5-6 atmospheres, otherwise there will be increased wear and premature failure.

In central highways, this figure is much higher - it can reach 15 atmospheres, and therefore, to reduce it, when connecting internal systems, pipes of smaller diameter are used.

Important. When the cross-section of the pipe is reduced, the speed of water flow increases, but its pressure decreases.
Therefore, if the pressure in the apartment is chronically low, you should consider increasing the diameter of the internal pipeline.

Why is it important to follow the parameters?

Compliance with standards plays a very important role , since only in this case is the normal functioning of household appliances connected to the water supply system possible. Many of them, such as washing machines, dishwashers, and hot tubs, simply will not work when the pressure is reduced to the minimum.

An increase in water pressure also negatively affects the operation of household appliances and plumbing equipment. Only in this case the load increases too much.

And as a result, equipment will fail faster, as well as particularly sensitive elements of the water supply system. In addition, leaks are possible in this case.

What is the power in the DHW and cold water systems?

The water pressure in multi-storey buildings connected to the central water supply network is not constant.

It depends on factors such as the number of storeys in the building or the time of year - so in the summer season, especially in multi-storey buildings, the lack of cold water becomes especially noticeable, which at this time is used for watering house or garden plots.

Municipal services in practice try to keep the level at an average of 3-4 atmospheres, although not always successfully. The minimum indicators at which the pipeline of a house can function (for both cold water supply and hot water supply) are 0.3 bar per floor.

The pressure of hot and cold water supply is slightly different in favor of the latter (a difference of up to 25% is allowed).

This is explained simply - cold water is used more actively, since it is needed for the functioning of the sewage system. Therefore, the maximum indicators for cold water supply will be 6 atmospheres, and for hot water supply – 4.5 atmospheres.

Some features of autonomous water supply systems

Autonomous water supply systems are called pipelines that are connected to a well or well. This moment determines the following:

1. There is a need to lift water from the well. Significant problems may arise in this area.
2. The pipeline system can be quite extensive. This point determines the difficulties in providing proper pressure for remote areas.

In addition, experts identify two main problems associated with autonomous water supply systems:

1. One should take into account the fact that a well can create problems not only with maintaining high pressure, but even maintaining a minimum value. With prolonged consumption of water, its level in the well drops significantly. That is why an expansion tank is installed, which is designed to maintain the proper indicator at a time of high load in the system.
2. If the water level in the well is high, it will be pumped constantly, which will cause a pressure increase of more than 6 atmospheres. As a result, a leak may occur and the installed equipment may malfunction.

The problem with a high score can be solved in a variety of ways. Let's take the following recommendations as an example:

1. Selecting a pump with a power rating that corresponds to daily water consumption. Many manufacturers indicate what capacity a particular pump has. It is worth remembering that with increasing pump power, electricity consumption increases significantly. Therefore, purchasing the most powerful pump or station is not a recommendation for all cases.
2. An electrical type control system can be installed. The water supply is often powered by an installed pressure gauge. The device can signal the motor to turn it on or off depending on what indicators are being read.

But the task of increasing the pressure in the system is more complex. To achieve this, a variety of equipment is installed. Don't forget that if you design your system correctly, you can avoid excess resistance. So some sections can be connected in parallel, others in series. It is important to select the correct pipes in terms of cross-sectional diameter and wall thickness.

What indicators are considered the norm (according to GOST, SNiP)?

Water supply is regulated by the following regulations:

• SNiP2.04.02-84;
• SNiP2.04.02-85;
• GOST 356-80;
• Decree of the Government of the Russian Federation No. 354.

In accordance with these documents, the free pressure in the water supply network at the entrance to the building directly depends on its number of storeys - for one-story buildings this figure is equal to 1 atmosphere, which corresponds to 10 meters of water pressure.

In multi-storey buildings this value increases by 4 meters for each floor of the building. At night, the incoming pressure can be reduced to 3 meters.

The pressure of cold water should be in the range from 0.3 to 6 atmospheres, hot - from 0.3 to 4.5.

Attention. According to clause 2.28 of SNiP 2.04.02-84, the maximum pressure at the entrance to the water supply network of a multi-storey building cannot exceed 60 meters of water column (6 atmospheres).
Otherwise, you should install pressure regulators or use zoning of the water supply network.

What's normal?

Although the specified SNiP contains standards for apartment buildings, owners of dachas and cottages can also rely on them.

For hot water

According to standards, this figure is 4-4.5 bar . It reaches this value in centralized highways, and this is what owners of private houses should strive for.

This is sufficient for most plumbing fixtures and does not require the purchase of fittings with enhanced performance.

For cold

In this case, the normal value for city apartments is 4-5 bar. But for autonomous water supply, when the pipeline is supplied with a less powerful pressure pump, the value can drop to 1.4-2.8 bar. But the optimal value is still considered a level of 4 bar .

How to find out power: step-by-step instructions

The most accurate way to determine the pressure of a water supply system can be a built-in pressure gauge - it is installed at the entrance to the internal network immediately after the shut-off valves with a filter.

If such equipment is not installed, then you can make a portable analogue yourself.

For this you will need:

• pressure gauge up to 6 atmospheres;
• threaded extension;
• adapter (if necessary);
• fumlenta;
• adjustable wrench.

Work order:

1. A threaded extension is attached to the pressure gauge, onto which an adapter is attached (if necessary). To ensure the accuracy of measurements, the joints are sealed using fume tape.
2. Disconnect the watering can from the shower hose and screw on the previously prepared pressure gauge; the connection is sealed with fume tape.
3. Fully open the shower valve and take readings from the pressure gauge.

Reference. During testing, for the accuracy of readings, you cannot use other plumbing fixtures: washing machine, sink, toilet, etc.

This method is the most accurate, however, if you urgently need to know the pressure, but there is no pressure gauge at hand, then you can use another, albeit less accurate, method: determining the pressure by water flow.
You will need:

• three-liter jar;
• stopwatch.

Measurement procedure:

1. A 3-liter container is placed under the tap, which is previously opened to full capacity.
2. At the same time, time is recorded on a stopwatch and how long it will take to fill the container.
3. The obtained time is checked against the tabular data and the pressure is set.

Table: dependence of pressure on water flow:

The video clearly shows how you can measure water pressure yourself:

Reasons for the decline

If the relay and pressure regulator are faulty, a sharp decrease or increase in load will be felt. Also, a complete lack of water supply or pressure surges cannot be ruled out.

As such, the control board is quite simple and durable. But, over time, the contact points oxidize and the shell loses its properties.

A pressure sensor that has failed can cause a short circuit.

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The membrane located in the compensating tank is damaged. And without this very important element, the water supply system will not be able to work normally.

The pressure switch is able to operate normally only within a certain scale, which is ensured by the contraction and stretching of the rubber bulb.

If it breaks, it will be immediately visible by the water pressure. The system will begin to operate in the wrong order.

Due to failure of the “on-off” cycles, the pump will fail. The bulb must not only be replaced with a new one, but also the reason for its failure must be found.

A large amount of sand, silt, and dirt can be washed into the compensating tank.

This rarely happens, but if such a nuisance does occur, it may happen that the entire system refuses to function normally.

The holes and wells are sometimes heavily silted. When the pump is suspended, it may break off and fall to the bottom.

In this case, water will be supplied to the system with sand and silt. This will cause clogging of the accumulator.

As a result, pressure surges will begin. If the cause is not corrected in time, sand will end up in pipes throughout the house.

Due to the limited burnout of the motor winding, the pump may break down.

The body of the product should be regularly checked for cracks, chips and traces of rust.

The cause of the pressure drop in the system may be a check valve.

If it is damaged, water will return back to the well or well, and this will cause a decrease in pressure.

There are several other reasons for poor pressure - improperly installed water supply system, failure to comply with operational requirements, frequent equipment breakdowns, and water supply features.

Any of the above reasons must be eliminated. And you can increase the pressure of the liquid substance in the pipes with the help of modern high-tech equipment.

How to calculate the loss?

Loss of pressure in the water supply network occurs for the following reasons (blockages and rust of pipes are not considered):

1. Pipe resistance in straight sections.
2. Local resistance (bends, valves, etc.).

For the convenience of calculations, there are online calculators that in a matter of seconds allow you to find out the level of pressure drop in the pipeline. You can also use special tabular data to solve this problem.

Calculation on straight sections

To calculate losses you need to find out:

• water consumption;
• pipeline material, its diameter and length.

Select the desired value in the table and find out the amount of pressure reduction.

Tabular data for polypropylene pipes; for metal pipes, a correction factor of 1.5 must be added to the calculations. If the pipe length is less than 100 meters, then the result is multiplied by the length factor. So for a metal pipe with a diameter of 50 mm, a length of 35 meters and a water flow rate of 6.0 m³/h, the following result will be obtained: 1.6 * 0.35 * 1.5 = 0.84 mvs.

We recommend an article on the topic

How to determine water flow by pipe diameter and pressure?

In places

Losses also occur at turns and bends of the pipeline, as well as at the locations of shut-off valves and filters.

There is a special table for calculations; to use it you need to find out the speed of water flow in the pipe - this is calculated as follows: the flow rate must be divided by the cross-sectional area of ​​the pipe.

In this table, the data is indicated in centimeters of water, and therefore it is obvious that pressure losses at local resistances are not critical and are not of fundamental importance for small networks.

What devices does the water supply system consist of?

Before calculating the pressure indicator and considering the established standards, you need to pay attention to what elements the system consists of. The classic water supply of a country house is represented by the following elements:

1. Ball valves. Locking mechanisms are an integral part of the water supply system. Why ball valves? There are quite a few reasons, the main one being the high reliability of the design.
2. Pressure gauges. This design is intended specifically for measuring pressure in the system. It is necessary to install pressure gauges in order to monitor the operation of the entire system.
3. Mesh filter for coarse cleaning.
4. A compressor that creates pressure in the system.
5. Fine filter. In order to improve the quality of water supplied to the house, a similar element is installed.
6. Check valve. This design is designed to prevent reverse flow in the event of a significant drop in pressure in the system.
7. The relief valve is designed to reduce the pressure in the pipe if critical values ​​are reached.
8. The expansion tank is designed to temporarily store water when the relief valve is opened.
9. Drain taps are installed before the consumer. This element is necessary in order to shut off the pipeline and drain water while servicing the system or performing repair work.
10. Thermometer for temperature control.

It is worth considering that as the length of the pipes increases, the pressure in the system increases significantly. Other elements, for example, filters, have the same effect on the pressure indicator. In addition, all elements of the system must also withstand pressure.

How to plug a pipe with pressurized water?

Putting a plug on a pipe is not a tricky thing if you do it without pressure.

But when the water cannot be turned off, many will think that it is impossible to do so. However, it is not.

It will not be possible to install a regular plug , since the strong pressure will not even make it possible to attach it to the thread.

But if you use a regular water tap instead, everything will work out.

The method is to switch the tap that will plug the pipe into open mode - water will pass through it and thereby make it possible to attach it to the threads of the pipe. As soon as the plug valve is attached and tightened a few turns, it can be closed.

Before work, you need to make sure that nothing will interfere with the work , and also prepare a container for collecting water and a rag for cleaning (so as not to drown your neighbors).

This method can be used even if the pipe to be plugged is without a thread - then you need to put a flexible hose on the plug valve that fits onto the pipe.

The tap, as in the first case, must be fully opened, and the hose must be placed on the pipe - it must be secured with one or two clamps. After this, you can finally turn off the water.

Important. This method cannot be used to plug hot water pipelines without completely shutting off the system.

Creating and maintaining pressure in an autonomous water supply system

The problem of excess pressure is quite rare, so let's talk about how to increase the pressure in the water supply to an acceptable level. Both in a private house and in a city apartment, you can find the opportunity to do this if you include special pumping equipment in the system (see High-pressure water pump for a private house).

Features of autonomous water supply

An autonomous water supply differs from a centralized one in the following features:

• Before supplying water to the house, it must first be raised to the surface from a well or well. What is part of the pump power spent on?

Autonomous water supply schemes with surface and submersible pumps

• Ensuring the standard pressure in the cold water supply system is required for all points that are located at different distances from the unit creating the pressure and can be located at different heights.

Internal wiring diagram in a private house

• The water source may have a flow rate that is too low to maintain normal pressure in the network for a long time. As long as there is water, the liquid will flow with good pressure, but as the well empties, it will weaken, and then the flow of liquid into the system will stop altogether.

The lack of water in the tap is most often due to low productivity of the source

• If there is enough water in the source, but the pump is too powerful, constant supply under high pressure can lead to premature wear of the system.

Almost all of the problems listed are easily solved by the correct selection of water-lifting equipment. Except for the one associated with insufficient pressure.

How to optimize water pressure

There are several proven methods to solve this problem:

• You can include a booster pump in the system, which will forcibly increase the pressure in it. It makes sense to do this only if there is sufficient water in the source, but it comes to remote or high points of consumption, having lost most of the pressure along the way. Such pumps can be controlled manually or automatically. The second method is preferable, since the automation itself will control the start and stop of the pump when needed.

Photo of a pressure boosting pump

For reference. Such pumps can also be installed in apartments of multi-storey buildings. But in this case, you risk leaving your lower neighbors completely without water.

• If the flow rate is insufficient, using a booster pump will only aggravate the problem. In this case, only a pumping station with a sufficiently large reservoir for storing water will help solve it. It works according to the following principle: while there is no water supply, the pump pumps water into the reservoir. It is a hydraulic accumulator (see Hydraulic accumulators for water supply: overview of varieties, nuances of selection and configuration), which, due to the presence of two cavities (water and air), creates pressure in the cold water supply system - the norm is set by the homeowner himself. After the accumulator is filled, the pump is turned off, and in the meantime the well is replenished. When the tap is opened, water enters the system from the reservoir at a given pressure. When it drops to the minimum set value, the pump turns on again and pumps water.

Water supply diagram with pumping station

Install the equipment only in a warm, dry room

Connection diagram for hydraulic accumulator

Tank pressure measurement

Hydraulic accumulator device

Scheme with additional storage capacity

• Another method involves using a large storage capacity. If you place it at the highest point of the house (in the attic or attic), it will be filled by the main pump, as in the previous case, and supplied to the consumer by gravity. But in this case it is unlikely to achieve decent pressure. It is better to buy an additional pump that will pump water from the barrel. Then it can be installed anywhere, even in the basement.

Installation of water supply with storage tank

It is important! The storage tank must be equipped with float valves, which will turn off the pump when it is filled and prevent overflow.

Formula for calculating water pressure in a multi-story building

Before presenting the formula for calculating water pressure, it is necessary to clarify:

• 1 bar = 1.019 atmospheres;
• 1 bar = 10.19 meters of water column (m w.s.);
• 1 atmosphere = 0.98 bar;
• 1 atmosphere = 10 m altitude

Let's consider the formula based on measurements in meters of water column: 10 m w.s. + (4 m x N) , where: - 10 m h.s. – this is the minimum pressure supplied to 1 MKD; — 4 m – accepted floor height; — N – number of floors of the apartment building.

For example, let’s calculate the pressure with which water should be supplied to a 9-story building: 10 + (4 x 9) = 46 (meters of water column), which is approximately equal to 4.6 atmospheres.

Varieties of quantities

In accordance with GOST, there are several types of basic parameter:

• PN (nominal pressure). It represents the period that a water pipe can last at maximum pressure. The temperature should not exceed 20 degrees. Steel lasts 20 years, plastic - 50.
• Pp (working). Equals the maximum excess. In this case, the pipeline elements can operate for a specified period of time without interruptions or malfunctions. Most often it is set at 20°C.
• Rpr (trial). Displays the excessive value set at the time of test activities. The reliability of connections and the strength of the structure are checked.